Concept 29.1 Multicellular Animals Require a Stable Internal Environment

SLUH – Bio 431/AP Bio – Pham Chapter 29 RG 29 – Physiology, Homeostasis, and Temperature Regulation

Concept 29.1 – Multicellular animals require a stable internal environment

1. What is interstitial fluid?

2. What is a tissue?

3. There are FOUR types of tissues. For each, give examples, the general function, and where you would find each type.

Tissue Type Example General Function Locations Epithelial cuboidal simple columnar simple squamous stratified squamous Connective cartilage adipose blood bone fibrous connective loose connective Muscle skeletal smooth cardiac Nervous neurons glial cells

Concept 29.2 – Physiological regulation achieves homeostasis of the internal environment

4. Throughout the text, a common theme has been regulation of homeostasis by feedback loops. We discuss feedback loops again as we look at hormone levels. What is meant by a set point?

5. Describe an example of a negative feedback loop. Clearly identify the set point, the stimulus, and the response. 6. We sometimes say that in negative feedback “more gets you less,” and in positive feedback “more gets you more.” Describe an example of a positive feedback loop.

Concept 29.3 – Living systems are temperature-sensitive

7. What is thermoregulation?

8. Describe the difference between endothermy and ectothermy, and give an example of an animal that exhibits each.

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9. What is metabolic rate (MR)? What is basal metabolic rate (BMR)?

10. Why does MR of a mammal increases as Ta decreases, whereas MR of a reptile decreases as Ta decreases, in the range of Ta’s below 25°C (Fig. 29.5)?

Concept 29.4 – Animals control body temperature by altering rates of heat gain and loss

11. What are the FOUR processes by which heat is exchanged with the environment? Use this figure to name and explain each process.

12. Discuss how each of the following are involved in thermoregulation:

fur/feathers

adipose tissue

goose bumps Page 2 of 5 SLUH – Bio 431/AP Bio – Pham Chapter 29

vasodilation/vasoconstriction

panting/sweating

burrowing/sunning

13. Heat loss in extremities is reduced by countercurrent exchange. Use this figure to explain how it works.

14. If a mouse and a small lizard of the same mass (both at rest) were placed in experimental chambers under identical environmental conditions, which animal would consume oxygen at a higher rate? Explain.

Concept 29.5 – A thermostat in the brain regulates mammalian body temperature

15. What is the role of the hypothalamus in temperature regulation?

16. What are the evolutionary advantages of torpor and hibernation?

A Hibernator’s Thermostat (Textbook Figure 29.13)

The first demonstration that thermoregulatory responses in mammals are controlled by the temperature of the hypothalamus was shown using dogs. The experiment shown in Fig. 29.13 was done some years later on ground squirrels, which may seem to be unusual experimental animals. However, the question that drove these experiments had to do with hibernation (see Fig. 29.14), an amazing adaptation of these animals for surviving winter conditions.

During hibernation the body temperature of a ground squirrel drops close to that of its environment which under the snow in the mountains where these animals live might be 0oC. The question being asked was whether this drop in body temperature was a failure of thermoregulation and a return to a more primitive ectothermic condition, or whether these animals had a brain thermostat that could be adjusted over a broad range of temperatures and enable the squirrels to regulate their body temperatures Page 3 of 5 SLUH – Bio 431/AP Bio – Pham Chapter 29 at these low levels. The first part of the effort to answer this question was to investigate the properties of the brain thermostats of these animals when they were not hibernating. In the experiment shown in Figure 29.13, tiny stainless steel tubes were surgically implanted into the brains of ground squirrels in either side of the hypothalamus. By circulating water at different temperatures through these tubes and measuring the temperature of the hypothalamic tissue between the two tubes, it was possible to control the temperature of the squirrel’s brain thermostat. If the metabolic rate of the squirrel were measured at the same time, it was possible to correlate the heat production of the squirrel with the temperature of its hypothalamus.

The data below were recorded from an experiment in which the hypothalamus of a ground squirrel was randomly cooled (TH) while the animal’s metabolic rate (MR) was measured. TH is given in °C, MR is given in calories per gram of body mass per minute.

Plot the data and describe what it tells you about the properties of the hypothalamic thermostat.

Original Papers

Heller, H. C., G. W. Colliver, and P. Anand. 1974. CNS regulation of body temperature in euthermic hibernators. American Journal of Physiology 227: 576–582. http://ajplegacy.physiology.org/cgi/reprint/227/3/576

Heller, H. C. and G. W. Colliver. 1974. CNS regulation of body temperature during hibernation. American Journal of Physiology 227: 583–589. http://ajplegacy.physiology.org/cgi/reprint/227/3/583

Hammel, H. T, D. C. Jackson, J. A. J. Stolwijk, J. D. Hardy and S. B. Strømme. 1963. Temperature regulation by hypothalamic proportional control with an adjustable set point. Journal of Applied Physiology 18: 1146–1154. http://jap.physiology.org/cgi/reprint/18/6/1146

Links (For additional links on this topic, refer to the Chapter 29 Investigation Links.)

Howard Hughes Medical Institute: Ask a Scientist Page 4 of 5 SLUH – Bio 431/AP Bio – Pham Chapter 29 http://www.hhmi.org/askascientist/answers/why_do_we_feel_cold_when_we_have_a_fever.html